PLT 1 shows a refrigeration cycle which is provided with a cooling operation mode and a “dehumidifying heating mode” described hereafter and enables switching between them. The cooling operation mode is a mode where an inside evaporator which is arranged at the inside of the compartment is used to cool the air which is blown to the inside of the compartment to cool the passenger compartment. The “dehumidifying heating mode” of this PLT 1 is a refrigerant circuit wherein an inside evaporator, and an outside heat exchanger which exchanges heat of a refrigerant with the outside air are connected in parallel at the downstream side of the inside condenser. Due to this, the outside heat exchanger and inside evaporator are made to function as heat absorbers. The inside evaporator absorbs heat from the fan air for a dehumidifying action. The inside condenser reheats the fan air and vents it to the inside for a heating and dehumidifying action.
In this PLT 1, an embodiment of use of an evaporation pressure regulator 12 at the outlet side of the inside evaporator 2 is shown. In both the cooling operation mode and dehumidifying heating mode, refrigerant flows to the evaporation pressure regulator. As an evaporation pressure regulator (also called “EPR”), a spring type evaporation pressure regulator (as one example, Japanese Patent No. 2781064 etc.) has been used. This holds the evaporation pressure of the refrigerant inside the evaporator at a certain pressure or more to prevent formation of frost of the inside evaporator (freezing of the moisture from dehumidification). That is, if the evaporation pressure of the refrigerant inside the evaporator falls, simultaneously the evaporation temperature falls (on the isobaric line at the two-phase region on a Mollier chart, the temperature is also constant), so frost ends up being formed. Therefore, in the spring type evaporation pressure regulator, the evaporation pressure of the refrigerant in the evaporator is held at a constant pressure or more.
In PLT 1, in both the cooling operation mode and “dehumidifying heating mode”, the evaporation pressure regulator controls the evaporation pressure of the refrigerant in the evaporator to a predetermined setting or more so as to prevent frost. However, in the prior art, a well known spring type evaporation pressure regulator (EPR) was used, so there were the following problems.
(1) The fins or tubes at the air side are cooled by conduction of heat from the inside refrigerant temperature, so when the air which is blown is high in temperature, the temperature difference between the temperature of the fins or tubes and the inside refrigerant temperature becomes large. In a spring type evaporation pressure regulator, the evaporation pressure is set to a constant pressure and control cannot be performed to lower the evaporation pressure (that is, evaporation temperature), so in the summer etc. when the air which is blown is high in temperature, the fins or tubes become high in temperature and the vented air temperature also ends up becoming higher. For this reason, it is not possible to suitably make use of the cooling capacity.
(2) The spring type evaporation pressure regulator uses a valve element (piston) which adjusts the refrigerant flow rate and a coil spring which biases the valve element in the closing direction. If the refrigerant flow rate is large, the opening of the valve element becomes larger. This means compressing the coil spring (opening of valve element and spring pressure are proportional). That is, the evaporation pressure of the refrigerant rises. Conversely, if the refrigerant flow rate is small, the opening of the valve element becomes small and the evaporation pressure also becomes low. For this reason, in order to prevent formation of frost of the evaporator, the setting has to be determined, when refrigerant flow rate is small, i.e., where the evaporation pressure (evaporation temperature) becomes the lowest. By doing this, in the summer season etc. when the refrigerant flow rate is large, the opening of the valve element becomes large and the evaporation pressure (evaporation temperature) also ends up becoming high. For this reason, the vented air temperature also ends up becoming higher, so it is not possible to suitably make use of the cooling capacity. That is, when the flow rate is large, inherently, if changing to a target value of a lower refrigerant temperature, a suitable cooling capacity should be able to be realized, but that is not so.
(3) When detecting the vented air temperature from the evaporator and using control to adjust the amount of discharge refrigerant of the compressor, if there is a spring type evaporation pressure regulator, the vented air temperature no longer falls to the set evaporation pressure (set evaporation temperature) of the evaporation pressure regulator or less. For this reason, even if the cooling load falls, the vented air temperature does not fall, so the speed of the electric compressor and the discharge capacity of the variable discharge compressor do not fall, the power increases more than necessary, and the COP ends up falling. Further, the fan air flow also does not fall and blowing of air continues unnecessarily.
(4) The spring type evaporation pressure regulator closes at a set pressure or less (usually, saturation pressure of HFCl34a at 0° C. of 292.8220 kPa[abs] or less). For this reason, when filling refrigerant in the refrigeration cycle, the inside is evacuated to discharge the air, but if the evaporation pressure regulator closes, there is the problem that a long time is taken for evacuation.
(5) If gas leakage etc. causes a drop in the amount of refrigerant in the refrigeration cycle, the liquid refrigerant in the accumulator disappears, the pressure in the evaporator drops, the opening of the spring type evaporation pressure regulator is reduced, and the compressor inlet pressure also falls. Due to this, there is the problem of a rise in the degree of overheating of the refrigerant which is sucked into the compressor and a rise in the discharge temperature due to an increase in the compression ratio.
(6) In a cycle which switches between cooling and heating, if a dehumidifying operation is not required at the time of heating, sometimes the evaporator inlet is closed by a solenoid valve, expansion valve, etc. to prevent refrigerant from flowing to the evaporator. When the compressor inlet pressure is low, the spring type evaporation pressure regulator automatically closes, so refrigerant pools inside the evaporator and sometimes the amount of refrigerant in the accumulator becomes insufficient. Further, when the air which is blown to the evaporator changes from the outside air to the inside air and the evaporator is heated, the refrigerant at the inside of the evaporator rapidly evaporates and the refrigerant flow rate increases, so there is the problem that fluctuations in vented temperature and fluctuations in compressor power occur.
Furthermore, with the cycle configuration of PLT 1 where different operation modes such as cooling and heating are switched between, pluralities of expansion valves and evaporation pressure regulators have to be used. Not only was there a problem in the increased number of parts and mountability, but also interference occurred between the evaporation pressure regulator and control for adjusting the amount of discharge refrigerant of the compressor.